1 Water covers about 70% of the Earth's surface. Three percent is freshwater, and the remaining 97% is saltwater. Freshwater habitats come in an array of forms. Lakes, rivers, and wetlands are three different types of the freshwater biome.2 By definition, lakes are bodies of standing water that lay inland. Some lakes are so large that we simply don't call them "lakes." Instead, we call them "seas." Even more confusing is that not all lakes are freshwater lakes. The Caspian Sea of Central Asia is the largest lake on Earth. It is also a saltwater lake. The Caspian Sea covers a vast expanse of about 143,300 square miles. The saline concentration in the Caspian Sea is close to one-third of that in oceans. Lake Baikal is another impressive lake that is worth mentioning. Situated in Siberia in Russia, Lake Baikal earns the distinction as the world's deepest lake. The deepest point in Lake Baikal is over 5,300 feet! Furthermore, it is estimated that nearly one-fifth of the Earth's freshwater comes from Lake Baikal!3 Unlike lakes, rivers are bodies of flowing water that usually exit into oceans or seas. The headwater is where a river begins. It can be a glacier, a snow-capped mountain peak, a lake, or a spring. Traveling down slope, a river may be joined by other rivers, creeks, or streams along the way. The path that a river flows through is its channel. The region on either side of the channel is the river's floodplain. About 4,200 miles long, the Nile River of Africa is the longest river on Earth. The first runner-up is the Amazon River of South America (4,000 miles). The second runner-up is the Yangtze River of Asia (3,965 miles).